It is often advantageous to wash laundry in cold water (e.g., temperatures from about 2-24.degree. C.). Washing in cold water generally conserves energy, and therefore costs less money than washing in warm water. Other advantages include potentially less damage to clothes.
Such advantages must often be balanced against the fact that detergents tend to form residues in cold water. Such residues are only slowly soluble in cold water. As a result, efficacy may be lost because the active ingredients are not fully in solution. Also, residues may remain at the completion of automatic washing cycles requiring additional work to clean automatic washing machines.
Winston et al. (U.S. Pat. No. 4,265,790) substantially eliminated the problem of cold water residue of silicate containing compositions by replacing fine, granular silicate with coarse, granular silicate in a dry blended laundry detergent. Muchow et al. (U.S. Pat. No. 3,213,029) improved the solubility of granular compositions containing chlorocyanuric acid by providing dense, physically stable, granular compositions.
However, the compositions of the prior art have not proven entirely satisfactory as they generally address the solubility of a specific ingredient in tepid water. Residues still generally form at very cold water temperatures (e.g., temperatures from about 2-12.degree. C.). This is due to the fact that particle size or density alone will not completely determine cold water solubility. Furthermore, the prior art does not teach or disclose non-residue compositions for the broad class of detergents comprising large amounts of carbonate and/or bicarbonate builders. Also, formulations containing high levels of hydratable ingredients exhibit extremely poor solubility in cold water. These are problems not addressed by the prior art.
It has now been discovered that cold water residues will not form in detergents comprising coarse particles having a high bulk density provided the particle diameter to density ratio criteria, as disclosed herein, is applied. It has been found that for all detergent compositions there exist particle diameter to density ratios which will provide complete solubility in cold water. Whereas prior art has specified particle size or density restrictions, the present disclosure requires only that these parameters exceed a minimum ratio. This is a surprising result as one trained in the art would hesitate to create large, dense detergent particles knowing the potential for insolubility. Conceptually, formulas comprising small granules, with large surface area, should dissolve rapidly.